1. Field of the Invention
The present invention relates to a fluid bearing device that supports a rotating member by an oil film formed in a bearing gap. The fluid bearing device of the invention is suitably used in spindle motors of magnetic and/or optical information equipment such as HDDs, FDDs, CD- or DVD-ROM drives, MD or MO drives, polygon scanner motors of laser beam printers, or other small motors in various electrical equipment such as axial-flow fans.
2. Description of the Related Art
The motors mentioned above must satisfy various requirements such as high rotation precision, high speed, low cost, and low noise. Motor spindle bearing is one of the constituent elements that determine required motor performance. Fluid bearings, particularly dynamic bearings, are considered to have excellent characteristics in many respects with regard to the required motor performance and some have found actual applications in recent years.
Fluid bearings are generally classified into two categories: One is the dynamic bearing, which includes means for generating dynamic pressure of lubricating oil in a bearing gap. The other is the cylindrical bearing, whose bearing surface forms a true circle, and which has no such dynamic-pressure generating means.
A fluid bearing device incorporated in a spindle motor of a disk device such as a HDD or in a polygon scanner motor of a laser beam printer normally includes a radial bearing part for rotatably supporting a shaft member in a radial direction and a thrust bearing part for rotatably supporting the same in a thrust direction. Of these, at least the radial bearing part is a dynamic bearing having dynamic-pressure generating grooves in the bearing surface. These grooves are formed on either one of an inner peripheral surface of a bearing sleeve and an outer peripheral surface of the shaft member.
The bearing sleeve is normally fixed to the inner periphery of a housing by means of press-fitting or bonding. The housing is usually provided with a sealing member at its open end so as to prevent leakage of lubricating oil that fills the inside of the housing.
Various efforts have been made to enhance the machining and assembling precision of respective components constituting the fluid bearing device such as the housing, bearing sleeve, shaft member, and sealing member, so as to achieve high bearing performance for satisfying the increasingly demanding performance requirements of the information equipment industry. On the other hand, with the trend towards lower prices of the information equipment, the demands for cost reduction of such fluid bearing devices are intensifying.